Soldering of silicon to Invar for double-crystal monochromators

At the Brazilian Synchrotron Light Laboratory (LNLS), new double-crystal monochromators are under development for use at the new Brazilian fourth-generation synchrotron, Sirius. The soldering technique used for the double-crystal monochromators ensures the union of monocrystalline silicon with FeNi alloy, Invar36 (64Fe–36Ni) from Grupo Metal and Invar39 (61Fe–39Fe) from Scientific Alloys, through SnSb (92.8Sn–7.2Sb), SnCu (Sn–0.3Cu) and SnBiCu (Sn–1.4Bi–0.7Cu) alloys from Nihon Superior. Following soldering tests and quantitative analysis, the Invar39/SnBiCu/Si samples were selected using base materials coated with different depositions – gold and copper. X-ray diffraction identified the formation of intermetallic compounds, such as AuSn₂ and AuSn₄ in base materials coated with gold and Cu₃Sn and Cu₆Sn₅ with copper. Before thermal cycling, the average force obtained in shear tests was 1131 N with copper deposition and 499 N with gold deposition. After five consecutive thermal cycles from room temperature down to cryogenic temperature (−196.15°C), specimens with gold deposition presented cracks in the interface region and those with copper deposition showed no defects. Based on this, qualitative and semi-quantitative analyses of specimens with copper deposition were carried out by scanning electron microscopy and energy-dispersive spectroscopy techniques to identify the composition, distribution and morphology of the elements.